The present invention relates generally to welding and, more particularly, to a method and system of dynamically controlling operation of a wire feeder from feedback regarding actual wire feed speed of the consumable weld wire directly measured from the consumable weld wire as it is being delivered to a weld or welding gun.
MIG welding, also known as Gas Metal Arc Welding (GMAW), combines the techniques and advantages of Tungsten Inert Gas (TIG) welding's inert gas shielding with a continuous, consumable wire electrode. An electrical arc is created between the continuous, consumable wire electrode and a workpiece. As such, the consumable wire functions as the electrode in the weld circuit as well as the source of filler metal. MIG welding is a relatively simple process that allows an operator to concentrate on arc control. MIG welding may be used to weld most commercial metals and alloys including steel, aluminum, and stainless steel. Moreover, the travel speed and the deposition rates in MIG welding may be much higher than those typically associated with either Gas Tungsten Arc Welding (TIG) or Shielded Metal Arc Welding (stick) thereby making MIG welding a more efficient welding process. Additionally, by continuously feeding the consumable wire to the weld, electrode changing is minimized and as such, weld effects caused by interruptions in the welding process are reduced. The MIG welding process also produces very little or no slag, the arc and weld pool are clearly visible during welding, and post-weld clean-up is typically minimized. Another advantage of MIG welding is that it can be done in most positions which can be an asset for manufacturing and repair work where vertical or overhead welding may be required.
MIG systems generally have a wire feeder that is used to deliver consumable filler material to a weld. The wire feeder is typically connected to a power source that powers the driver motor(s) of the wire feeder as well as generate a voltage potential between the consumable filler material and the workpiece. This voltage potential is then exploited to create an arc between the filler material and the workpiece and melt the filler material and workpiece in a weld. The power source and the wire feeder may also be disposed in a common enclosure.
Typical wire feeders have a driven roller assembly for driving the consumable metal wire from a feed spindle through a welding gun for introduction to a weld. The drive mechanism in these driven roller assemblies typically includes a direct current (DC) motor or combination of DC motors to rotatably drive the feed spindle and deliver the consumable metal wire or filler material to the weld. Some wire feeders utilize a multi-motor drive configuration wherein a first motor delivers wire from the feed spindle so as to “push” it toward the gun. This motor is typically referred to as a “push motor.” Within this arrangement, the wire feeder also has a second motor to “pull” the wire from the push motor and drive it to the weld. Accordingly, this motor is typically referred to as a “pull motor.” Other wire feeders utilize only a single “push” motor to drive the filler material to the weld; however, it is often desirable to have a multiple motor arrangement whereby the motors act in concert to provide a relatively uniform delivery and a taut line of wire from the feed spindle to the welding gun.
For both single and multi-motor wire feeders, fixed control schemes are generally utilized to control operation of the motors. That is, whether through a direct user-input or indirectly set from other user-inputs, the motor(s) are controlled to deliver consumable weld wire at a given wire feed speed (WFS). This is particularly applicable for constant voltage systems where the WFS must be adjusted so as to maintain a constant weld voltage. As one skilled in the art will appreciate, if the voltage setting is fixed, there is an inverse relationship between WFS and weld voltage and, thus, an increase in WFS results in a drop in weld voltage. More generally, however, there is a proportional relationship between WFS and weld voltage. In this regard, increasing WFS requires a higher weld voltage to maintain a stable arc. Conversely, lowering the weld voltage requires a drop in WFS to maintain arc stability. Whether voltage is to remain fixed or vary, it is critical that the speed at which consumable weld wire is delivered to the weld be precisely controlled to avoid blow-through or incomplete welding, and maintain arc stability.
As such, wire feeders typically include an encoder that is designed to provide feedback as to the velocity or rate by which the feed spindle is delivering filler material to the weld or welding gun. That is, a controller or other controlling device causes the motor(s) to deliver wire at a given velocity and the encoder provides feedback to the controller as to whether the motor(s) are causing delivery of the wire at the given velocity. As such, the encoder indirectly monitors the speed by which wire is delivered to the weld or welding gun. That is, WFS is determined from monitoring the motor(s) or the feed spindle, but not from the wire itself. As a result, control of the motor(s) is rigidly based on a presumed WFS.
Other WFS monitoring systems are designed to determine WFS directly from the feed spindle as consumable weld wire is pulled therefrom and delivered to the weld, but such systems also suffer from drawbacks. These systems generally include an idler roller proximate the feed spindle that is turned by direct contact with the feed spindle as it rotates. These contact-based systems, while reasonably accurate, cannot consider changes in WFS once the fee spindle passes the roller. As a result, the WFS determined from feedback from the roller may be inconsistent with the actual speed by which wire is delivered from the welding gun to the weld. This inconsistency can affect welding performance as, for example, the weld voltage may exceed a desired level because the believed WFS is faster than actual WFS. In short, conventional WFS monitoring systems fail to account for effects on WFS that occur at or near the welding gun.
It would therefore be desirable to have a system and method capable of accurately measuring WFS directly from the consumable weld wire as the wire is being delivered to a weld or welding gun, but also take into account effects on WFS that occur at or near the welding gun.